The present invention relates to a motor-driven disk brake for generating a braking force by means of a torque of an electric motor.
As a brake apparatus for a vehicle, such as an automobile, there has been known a so-called xe2x80x9cdry brakexe2x80x9d apparatus which generates a braking force by means of an output of an electric motor, without using a brake fluid.
As an example of a dry brake apparatus, there can be mentioned a motor-driven disk brake disclosed in Unexamined Japanese Patent Application Public Disclosure (Kokai) No. 60-206766. In this disk brake, rotation of the motor Is converted to a reciprocating motion of a piston by means of a ball screw mechanism and brake pads are pressed against a disk rotor by the piston, to thereby generate a braking force. In a motor-driven disk brake of this type, a pedal pressure applied to the brake pedal (or an amount of displacement of the brake pedal) is detected by a sensor. A controller controls rotation of the motor according to results of detection by the sensor, to thereby obtain a desired braking force.
In the above-mentioned motor-driven disk brake, it is relatively easy to incorporate servo control, antilock control, traction control and vehicle stability control by using various sensors for detecting the condition of the vehicle. For example, a rotational speed of each vehicle wheel, a speed and an acceleration of the vehicle, a steering angle and a lateral acceleration of the vehicle are detected by the sensors, and rotation of the motor is controlled, based on results of the detection.
However, the above-mentioned conventional motor-driven disk brake utilizing a ball screw mechanism poses the following problems That is, for obtaining a sufficiently large braking force by increasing a thrust of the piston, It is necessary to increase the output of the motor or to increase a transmission ratio of the ball screw mechanism by reducing a lead thereof. However, for increasing the output of the motor, a large motor must be used and power consumption Inevitably becomes high. On the other hand, a reduction in the lead of the ball screw mechanism is limited, depending on the diameters of the balls, so that a sufficiently high transmission ratio is difficult to obtain.
As a countermeasure, it is considered to increase the transmission ratio of the ball screw mechanism by reducing the length of the groove of the ball screw mechanism to a length of less than 1 pitch, so as to set the lead of the ball screw mechanism as being smaller than the diameters of the balls. In this arrangement, however, no circulation of the balls occurs within the groove, so that for obtaining a secure operation of the ball screw mechanism, it is necessary to arrange the balls so as not to fill the groove and provide a space containing no balls. In this case, the thrust is not generated uniformly in the entire groove, so that the load due to a bending moment is generated and the portion for supporting the balls must be high. This leads to problems, such as an increase in weight of the supporting portion and high cost of production. Further, the structure of the ball screw mechanism is special, so that processing cost becomes high.
Further, in the above-mentioned motor-driven disk brake, from the viewpoint of saving the space for Installing the ball screw mechanism and the motor, a floating type caliper is employed so that one brake pad is pressed against the disk rotor by the piston, and the other brake pad Is pressed against the disk rotor by moving the caliper due to a reaction force. Therefore, it is necessary to obtain high rigidity of a portion providing a thrust transmission path from a thrust generating mechanism to a claw portion of the caliper Therefore, the case for the electric motor is required to have a large wall thickness, leading to an increase in weight of the case. Further, in the motor-driven disk brake utilizing a floating type caliper, at the time of removing the braking force, the brake pad on a side of the claw portion does not smoothly return to its original position, so that dragging of the brake pad is likely to occur. Further, a transmission mechanism such as the ball screw mechanism and the electric motor are connected to the caliper body, so that ease in assembling of the transmission mechanism and the motor must be fully considered.
In view of the above, the present invention has been made. It is an object of the present invention to provide a motor-driven disk brake in which a high transmission ratio can be obtained without generating a high load due to a bending moment and high rigidity of a portion providing a thrust transmission path can also be obtained and which is capable of preventing dragging of the brake pads. It is another object of the present invention to provide a motor-driven disk brake which can be easily assembled.
According to the present invention, there is provided a motor-driven disk brake comprising, a first brake pad and a second brake pad disposed at opposite sides of a disk rotor, a piston disposed so as to face the first brake pad, a claw portion extending over the disk rotor and facing the second brake pad, an electric motor disposed in the vicinity of the piston, and a ball ramp mechanism for converting rotation of the electric motor to a linear motion so as to reciprocally move the piston, to thereby enable application and removal of a braking force relative to the disk rotor by means of the brake pads, the ball ramp mechanism being disposed between the first brake pad and the electric motor.
By this arrangement, the ball ramp mechanism can be disposed in the vicinity of the claw portion Therefore, it is possible to secure sufficient rigidity of a brake case providing a thrust transmission path from the ball ramp mechanism to the claw portion, even when the wall thickness of the brake case is reduced. This leads to a reduction in weight of the disk brake.
According to the present invention, there is also provided a motor-driven disk brake comprising a first brake pad and a second brake pad disposed at opposite sides of a disk rotor, a piston disposed so as to face the first brake pad, a claw portion extending over the disk rotor and facing the second brake pad, an electric motor for rotating a rotor, a first ball ramp mechanism for converting rotation of the rotor to a linear motion so as to reciprocally move the piston, and a second ball ramp mechanism for converting rotation of the rotor to a linear motion so as to reciprocally move the claw portion.
The first and second ball ramp mechanism include, a central disk which rotates with the rotor, the central disk having two end surfaces, a first disk connected to the piston, the first disk being disposed so as to have a surface thereof facing one of the two end surfaces of the central disk, a second disk connected to the claw portion, the second disk being disposed so as to have a surface thereof facing the other of the two end surfaces of the central disk, the surfaces of the central disk and each of the first and second disks facing each other including ball grooves, and balls provided between the ball grooves.
By this arrangement, when the rotor is rotated by the motor, the first and second ball ramp mechanisms move the piston and the claw portion, respectively, to thereby enable the brake pads to be pressed against and removed from the disk rotor so as to apply and remove or release a braking force. In this instance, a thrust is uniformly transmitted by means of the balls provided between the ball grooves in the central disk and the first and second disks of the first and second ball ramp mechanisms.
Further, the present invention provides a motor-driven disk brake comprising a first brake pad and a second brake pad disposed at opposite sides of a disk rotor, a piston provided in a caliper body so as to face the first brake pad, a claw portion fixed to the caliper body and extending over the disk rotor so as to face the second brake pad, an electric motor provided in the caliper body, and a ball ramp mechanism for converting rotation of a rotor of the electric motor to a linear motion so as to reciprocally move the piston.
The ball ramp mechanism comprises a fixed disk disposed between the disk rotor and the electric motor and fixed to the caliper body, a movable disk disposed between the disk rotor and the fixed disk and connected to the piston, the movable disk having a surface thereof facing a surface of the fixed disk, and balls provided between ball grooves formed in the surfaces of the movable disk and fixed disk facing each other, the movable disk extending through the fixed disk and being connected to the rotor of the electric motor.
By this arrangement, when the rotor is rotated by the motor, the movable disk of the ball ramp mechanism moves the piston and presses one brake pad against the disk rotor, and the claw portion presses the other brake pad against the disk rotor due to a reaction force, thereby generating a braking force. In this arrangement, the ball ramp mechanism can be disposed in the vicinity of the disk rotor, making it possible to secure sufficient rigidity of a brake case providing a thrust transmission path from the ball ramp mechanism to the claw portion, even when the wall thickness of the brake case is reduced.
Still further, the present invention provides a motor-driven disk brake for applying and removing a braking force relative to a disk rotor by moving a pair of brake pads disposed at opposite sides of the disk rotor. The motor-driven disk brake comprises a caliper body, an electric motor provided in the caliper body, and a ball ramp unit connected to the caliper body, the ball ramp unit being adapted to move the brake pads by receiving power of the electric motor.
The caliper body includes a case for covering the electric motor, and a claw portion extending from the case over the disk rotor so as to face one of the pair of brake pads.
The ball ramp unit includes a piston facing the other of the pair of brake pads, a ball ramp mechanism for converting rotation of a rotor of the electric motor to a linear motion so as to reciprocally move the piston, the ball ramp mechanism including a fixed disk which is fixed to the caliper body by connecting the ball ramp unit to the caliper body, a movable disk connected to the piston and balls provided between the fixed disk and the movable disk, and a case for covering the fixed disk and movable disk in a circumferential direction thereof so as to accommodate the piston and the ball ramp mechanism as a unit.
Thus, the fixed disk, the movable disk and the balls of the ball ramp mechanism are accommodated in the case as a unit, so as to provide the ball ramp unit. Therefore, the disks and balls can be easily connected to the caliper body.
In this motor-driven disk brake, a pad wear compensating mechanism may be connected integrally to the ball ramp unit. By this arrangement, the pad wear compensating mechanism can be connected to the caliper body, together with the ball ramp mechanism.
Still further, the present invention provides a motor-driven disk brake comprising a first brake pad and a second brake pad disposed at opposite sides of a disk rotor, a piston provided in a caliper body so as to face the first brake pad, a claw portion fixed to the caliper body and extending over the disk rotor so as to face the second brake pad, an electric motor provided in the caliper body, and a transmission mechanism for converting rotation of a rotor of the electric motor to a linear motion so as to reciprocally move the piston. The rotor of the electric motor and the transmission mechanism are connected through the claw portion by assembling the transmission mechanism as a subunit, connecting the transmission mechanism to the inside of the claw portion and connecting the electric motor to the outside of the claw portion.
Thus, in the above-mentioned motor-driven disk brake, the transmission mechanism is assembled as a subunit. Therefore, the transmission mechanism can be easily connected to the caliper body. In addition, by connecting the transmission mechanism to the inside of the claw portion, the thrust from the transmission mechanism can be directly transmitted through the claw portion to the brake pads.
Still further, the present invention provides a motor-driven disk brake for applying and removing a braking force relative to a disk rotor by moving a pair of brake pads disposed at opposite sides of the disk rotor. The motor-driven disk brake comprises a piston facing one of the pair of brake pads, a claw portion extending over the disk rotor so as to face the other of the pair of brake pads, an electric motor spaced apart from the claw portion and disposed in the vicinity of an end portion of the piston, and a ball ramp mechanism for converting rotation of the electric motor to a linear motion so as to reciprocally move the piston, to thereby enable application and removal of a braking force relative to the disk rotor by means of the brake pads, the ball ramp mechanism being disposed between the claw portion and the electric motor.
Still further, the present invention provides a motor-driven disk brake for applying and removing a braking force relative to a disk rotor by moving a first brake pad and a second brake pad disposed at opposite sides of the disk rotor. The motor-driven disk brake comprises a motor mechanism portion, and a power transmission mechanism portion connected to the motor mechanism portion, the power transmission mechanism portion being adapted to move the brake pads by receiving power from the motor mechanism portion. The motor mechanism portion includes an electric motor and first case for covering the electric motor. The power transmission mechanism portion comprises a claw portion including a flange portion having an opening and a ball ramp unit inserted into the opening of the flange portion.
The ball ramp unit includes a piston disposed so as to face the first brake pad, a ball ramp mechanism for converting rotation of a rotor of the electric motor to a linear motion so as to reciprocally move the piston, and a second case for accommodating the piston and the ball ramp mechanism as a unit.
The claw portion is capable of extending over the disk rotor and facing the second brake pad when the ball ramp unit is inserted into the opening of the flange portion. The motor-driven disk brake further comprises a transmission device for transmitting power of the electric motor of the motor mechanism portion to the ball ramp mechanism of the power mechanism portion when the power transmission mechanism portion and the motor mechanism portion are connected by engaging the first case with the claw portion.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.